There 2 Oracle DB instances that have SGAs < 4Gb together, so the max-shm-memory is correct (5.5GB).
The DBs ran fine for a long period of time (years) with this setup. Recently I rebooted the server (clean reboot) and when the DBA tries to start both DBs, they get ORA-27102 error at startup (which basically means there's no enough memory).

Anyways, looking at http://docs.oracle.com/cd/E19683-01/817-1592/rmtaskproj-3/index.html , the conclusion is that the default project SHOULD be oracle.project , because I have a specific entry in this file:
bash-3.2# grep oracle /etc/user_attr
oracle::::project=oracle.project